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Old school leaf spring traction devices vs Cal Tracs

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Old school leaf spring traction devices vs Cal Tracs

Postby PackardV8 » Tue Apr 29, 2008 4:15 pm

Greetings, SpeedTalkers.

Really two leaf spring questions here:

1. Assuming an equal length of arm, front mounting point in vertical line with front spring eye and a rear mounting point equal distance above or below the axle center line, does the chassis know or care whether a traction bar is mounted below the axle or above the axle? An engineer told me it is always better to have the bar in tension rather than in compression. Another manufacturer told me the only reason traction bars mount below the axle is that is where the U-bolts are. Anyone can bolt them on the bottom. Few have the ability to weld a bracket on the top of the axle.

2. Is there bite magic in the CalTracs pivoting front mount versus a fixed front mount where say the front spring eye bolt was twice as ling and went through the front eye of the traction bar. Again, I was told the CalTracs pivoting mount is just a way to get a bit of compliance in the setup, as the traction bar and the spring move in different arcs and a fixed mount bar will bind.

I've run both types with some success, but would like to understand the theories involved.

thnx, jack vines
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Postby Larry Woodfin » Tue Apr 29, 2008 7:15 pm

Jack,

one thing to consider about mounting with the u-bolts. The original Cal-Trac design had to work within the NHRA Stocker rules, thus requiring a bolt on system. If John Calvert had not been constrained by the bolt on rule we might have seen a different design. I don't know that to be so but at the conception, his market was class legal cars.

Just food for thought.
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Postby Tuner » Tue Apr 29, 2008 10:28 pm

Have you seen the Mopar Chassis Book and what they called the “Leaf Link” as used on the Motown Missile `70 Pro Stocker? The leaf springs are clamped from the axle forward at each leaf tip and a solid link is above the axle. There’s more to it than just that, drawings and an explanation are in the book. The main leaf is heaver in the Mopar racing “Super Stock” spring pack.

My father taught me the “moonshiner’s trick” of clamping the leaf tips forward of the axle when he and his racing buddies put some on a Hudson Hornet circle track car in the early 50’s. Absolutely the best thing you can do for an early Mustang or Camaro if you want it to remain flexible enough in the rear to handle well in corners too. Clamping the leaves increases the rear roll stiffness and has to be balanced with a bigger bar in the front to keep it from being loose.

For the Camaro and Nova a good trick is to use the mono-leaf for a main leaf, cut the front eye off the multi-leaf main leaf so the front tip is right under the front spring eye bolt and also use 2 or 3 secondary leaves. The extra leaves are shortened or cut off behind the axle so the spring rate isn’t increased too much. Make solid clamps with 3/8” x 2” strap with two 3/8” bolts on each end as close to the springs as possible and don’t use the slippy stuff between the springs. This gives the strength of the larger main leaf with the axle wrap-up control of the clamped multi-leaf segment in front of the axle. A pinion snubber is a good thing. This method is too simple to please some people. :roll:
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Postby Horndog » Wed Apr 30, 2008 8:25 pm

Cal-Tracs are new technology.
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Postby af2 » Wed Apr 30, 2008 8:34 pm

Horndog wrote:Cal-Tracs are new technology.


What!!!!!

I say no more today!
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Postby Horndog » Thu May 01, 2008 10:48 am

af2 wrote:
Horndog wrote:Cal-Tracs are new technology.


What!!!!!

I say no more today!



LOL ........ :lol: :lol: :lol:

They work, what else needs to be said
:?: :?:
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Postby Tuner » Sat May 03, 2008 7:08 pm

I don’t see how the caltrac can control the axle in braking. Looks like a single purpose deal to me. Do people use them on the street? What happens when you try to stop and turn? After you go over the river and through the woods it just looks like a complicated way to have a slapper bar that only works in one direction. The main leaf still has to transmit the force from the tire patch to the front spring perch.
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Postby af2 » Sat May 03, 2008 10:35 pm

Tuner wrote:I don’t see how the caltrac can control the axle in braking. Looks like a single purpose deal to me. Do people use them on the street? What happens when you try to stop and turn? After you go over the river and through the woods it just looks like a complicated way to have a slapper bar that only works in one direction. The main leaf still has to transmit the force from the tire patch to the front spring perch.


Tuner, I was trying for days to say exactly what you said in 1 minute!( or 5 the way I type)!
There are better ones out there.
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Postby BLACK BART » Sun May 04, 2008 7:14 am

Jack, I believe the Cal-Trac design just locks the front of the spring up as if it were a solid member to prevent wind up. The upper and lower mounting holes just provide a stiffer or softer front spring half. The pre-load you put in the bars just gives you an earlier or later response to the movement of the axle when it starts to wind up. After much head scratching to figure it out myself, that was the conclusion I came to. If I'm out in left field I hope someone will please correct me.

Tuner, as was stated earlier by Larry Woodfin, the Cal-Trac design was developed for the NHRA Stocker rules. This means they were never intended to do anything but control axle wind up on acceleration since drag cars don't turn or brake like a road racer. This being said, you are absolutely correct in that they are a single purpose deal, but they do work well for the application they are intended for. I'm very interested in the mono leaf with clamped and cut multi leafs below it you talked about. I have a set of the split mono leaf springs from the Cal-Trac guys and will try those first, but the combination you mentioned earlier is very interesting to me as well. I have a few questions that may be relevant to this discussion about the mono leaf set up you talked about.

Running the individual leafs behind the axle, is this just for ride height?
Do you clamp any of the rear leafs or just let them ride with no clamps and separate on acceleration?
Mono leafs have no hole for the center pin, would it help to locate the hole farther forward like a Chrysler super stock spring when drilled, provided you have tire to body clearance?

Thanks, CJ
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Re: Old school leaf spring traction devices vs Cal Tracs

Postby cpmotors » Sun May 04, 2008 11:34 pm

PackardV8 wrote:Greetings, SpeedTalkers.

2. Is there bite magic in the CalTracs pivoting front mount versus a fixed front mount where say the front spring eye bolt was twice as ling and went through the front eye of the traction bar. Again, I was told the CalTracs pivoting mount is just a way to get a bit of compliance in the setup, as the traction bar and the spring move in different arcs and a fixed mount bar will bind.

I've run both types with some success, but would like to understand the theories involved.

thnx, jack vines



The advatange to the two mounting points is to change the Instant Center. It can make a big difference in how hard it hits the tires and where the "lift" or force is applied, effectively like a 4-link. The length adjustment is to preload the spring and has a big impact on traction. I doubt you can get the same affect with a fixed length bar thru the spring eye.
I use them on the street with great succes. They dont hang down and get in the way like slappers and make ride adjustments easy. Quite a few road racers also like them, as when the spring compresses on turns the cross bolt over the top of the spring is applied to increase "effective" spring rate. As far as braking forces, I dont see either one having any effectective change.

af2, what have you seen that you like better for a leaf spring car?
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Postby cjer » Mon May 05, 2008 3:26 pm

Tuner: Good info!
This is of interest to me and would like to try so I have some details questions:
(For the Camaro and Nova a good trick is to use the mono-leaf for a main leaf, )
Does this mean get a true monoleaf spring or to use the one main leaf of a multileaf spring?

(cut the front eye off the multi-leaf main leaf so the front tip is right under the front spring eye bolt)
Understood.

(and also use 2 or 3 secondary leaves.)
Any secondary springs? Any particular ones from a multi leaf pack?

(The extra leaves are shortened or cut off behind the axle so the spring rate isn’t increased too much.)
Assuming you only cut off the "secondary springs" and not the main leaf that is going to the front spring eye bushing?

How would all this compare to switching to Chrysler springs if it could be done?
Thanks.
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Postby Bubstr » Mon May 05, 2008 5:14 pm

I'm having a hard time seeing how a caltrack will change the instant center. The actual front mounting location of the spring or the bar does not change. the tire contact patch does not change. It could Stop the wrap up of the front spring half and even spread the load a bit on the most sever bend of the spring on a wrap up. It could even induce rear steer depending if they where set equal, but I can't see an I/C change. I can see a I/C change on a pinion snubber, depending on hight it's set at. There are different connecting points on a snubber.

The front half stacked spring is for wrap up control with out changing spring rate. If you take a leaf spring, for most of our uses, you can figure the front half is for wrap up control and the rear half is for rate.

The only ways I can see to change the instant center on a leaf spring is, 1 change front mount, 2 lowering blocks (ride hight up or down), 3 rearching or dearching springs, 4 pinion snubber, 5 shortening or lengthening rear shackles. Any thoughts on this?
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Postby BLACK BART » Mon May 05, 2008 10:10 pm

Bubstr wrote:
"I'm having a hard time seeing how a caltrack will change the instant center. The actual front mounting location of the spring or the bar does not change. the tire contact patch does not change. It could Stop the wrap up of the front spring half and even spread the load a bit on the most sever bend of the spring on a wrap up. It could even induce rear steer depending if they where set equal, but I can't see an I/C change. I can see a I/C change on a pinion snubber, depending on hight it's set at. There are different connecting points on a snubber.

The front half stacked spring is for wrap up control with out changing spring rate. If you take a leaf spring, for most of our uses, you can figure the front half is for wrap up control and the rear half is for rate.

The only ways I can see to change the instant center on a leaf spring is, 1 change front mount, 2 lowering blocks (ride hight up or down), 3 rearching or dearching springs, 4 pinion snubber, 5 shortening or lengthening rear shackles. Any thoughts on this?"







I would agree with all of this since the mounting point on the vehicle does not change and there is only one per side unlike a four link.

It's my belief that the two adjustment holes just make the front half of the spring act stiffer or weaker via the input from the rear mount when the axle tries to rotate. One adjustment just has more leverage than the other and pushes on the top of the spring harder so as to make the spring act stiffer.

That's the way I see it, but I would like to hear more from some of the real suspension experts on this subject, as I'm sure many others would too. CJ
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Postby cpmotors » Mon May 05, 2008 10:14 pm

I'll give it a shot to explain as I understand it but refer you to Dave Morgans Door Slammer: the chassis book for better reference.
For reference the instant center is the point the rear suspension rotates around.
As you stated the rear of the spring is for rate and the front is wrap control. But where does that control come from? The front spring eye. All force is transfered at this point. Slapper bars only stop the rotation of the axle and/or spring wrap. Force is still applied at the spring eye as a point of lift.
A fixed length bar, mounted either directly above or below the axle and intersecting at the spring eye is still applying its force at the mounting point. Effectively making it a ladder bar.
Cal-tracs make use of the lower "force transfer link" by turning the leaf spring into the upper bar of a four link , making the link the lower bar. Rotational force of the rear is now redirected into a forward and up motion around the front pivot point. (You could even argue that the spring is now in tension and the lower link is in compression.) With the lower link in the upper mount below the spring eye, the instant center is higher and farther back. With it in the lower mounting position, it moves the IC farther forward and lower.
The effects of changing the mounting points and therefore the IC are very apparent on how hard and fast separation of the rear end happens with the two different settings.
To see it another way, sketch out, as viewed from the side of the car, a leaf spring and mounts, axle tube, lower mount and transfer link, and the pivot with one hole directly behind and two holes directly below the spring eye.
Now using a straight edge, draw a line from the axle leaf mount point thru the spring, extending well past the mount point.
Now draw a second line from the lower mount below the axle to the upper mounting hole of the pivot point until it intersects with the first line. That point is now the effective instant center.
Now draw a third line from the lower mounting point thru the lower pivot point until that intersects with the first line. The effective instant is now farther forward and lower.
The front spring eye is still where the force is transfered, but the effective force is redirected.
Changing the front mount point of the spring ,up or down,will also change the IC.
Lowering blocks and de/re arching springs and shackle lengths will merely change the ride height of the rear of the car and therefore the Center of Gravity only.
Clear as Mud?
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Postby Bubstr » Tue May 06, 2008 3:02 am

Lowering blocks and de/re arching springs and shackle lengths will merely change the ride height of the rear of the car and therefore the Center of Gravity only.
Clear as Mud?[/quote]
Ok when ride hight is changed, the elevation of your front mounting point is also changed. as your rear end does not change, it has to change both the center of gravity and the instant center. The changing of ride hight is great for small adjustments even on ladder bars or 4 links in between holes.

I guess the part that stumps me is all force is applied to the front mounting point, no matter what bells and whistles. Now if we where to say that as it cut down spring wrap up it increased front half spring rate to help any anti squat that was present. I might be able to understand that. I keep thinking of the monkey that rides the bicycle on the tight rope with a big bird suspended below on a curved half circle perch. no matter how big the bird or what shape the perch the force is always straight down. It's impossible for the monkey to fall over because there is only one point of force. I guess that is the source of my mud.
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